Mecasermin
Recombinant human IGF-1 (Increlex) — the one IGF-1 product approved as a medicine, for growth failure in severe primary IGF-1 deficiency.
Mecasermin at a Glance
Mecasermin is recombinant human IGF-1 — the actual hormone, produced in the laboratory rather than an analogue of it. It is the only IGF-1 product approved as a medicine, licensed as Increlex for severe primary IGF-1 deficiency in children who do not respond to growth hormone. That approval matters beyond its own indication: it is the reference point against which the unapproved IGF-1 analogues sold as research chemicals should be read, and it comes with a real label, real trial data and a documented safety profile that they do not have.
History & Development
Mecasermin is not an analogue of anything - it is recombinant human IGF-1 itself, and it exists because a small group of children make growth hormone normally but cannot produce the hormone that growth hormone is supposed to trigger.
| First described | IGF-1 characterised as somatomedin C in the 1970s; recombinant product approved 2005 |
| Discovered / synthesised by | Not established in the sources consulted for this section |
| Institution | Not established in the sources consulted for this section |
| Origin | Recombinant form of the endogenous human hormone insulin-like growth factor 1 |
| Key patent | Not established in the sources consulted for this section |
| Assignee | Marketed by Ipsen; US product acquired by Eton Pharmaceuticals (2024) |
| Development status | Approved - FDA 30 August 2005 (NDA 021839, since deemed a BLA); EMA 2 August 2007 |
Discovery
The biology came first and the drug followed from a gap in it. Growth hormone does not act on bone directly; it instructs the liver to produce IGF-1, originally named somatomedin C, and IGF-1 carries out the growth signal. That two-step arrangement means a child can have entirely normal growth hormone and still fail to grow, if the second step is broken.
That is the condition mecasermin treats: severe primary IGF-1 deficiency, where growth hormone therapy cannot work because the problem lies downstream of it. Supplying IGF-1 directly bypasses the missing step. The originating laboratory and the specific development history of the recombinant product were not established in the sources consulted for this section.
Development & ownership
Mecasermin was approved by the FDA on 30 August 2005 under NDA 021839, as a Type 1 New Molecular Entity with priority review and orphan designation, and was deemed a BLA on 23 March 2020 under the biologics transition. The EMA authorised it on 2 August 2007 under exceptional circumstances - the pathway used when a condition is too rare for conventional trial evidence - and its orphan designation lapsed in August 2017 at the end of its exclusivity period.
A second product should not be confused with it. Mecasermin rinfabate (iPlex), a complex of IGF-1 with its binding protein IGFBP-3, was separately approved as BLA 021884 to Insmed on 12 December 2005; its European application was withdrawn in March 2007 after the CHMP concluded benefit had not been sufficiently demonstrated, and the product is discontinued.
The US product changed hands recently, acquired by Eton Pharmaceuticals in December 2024 and relaunched in January 2025.
How it reached the market
Mecasermin is a prescription biologic supplied through specialty channels for a rare paediatric condition, and it has never had a consumer market. Its significance here is as the reference point for the unapproved IGF-1 analogues - IGF-1 LR3 and IGF-1 DES - which are sold for muscle growth. Mecasermin is the only IGF-1 product with a real label, real trial data and a documented safety profile; those analogues borrow its biology without any of that record.
What It's Used For
Mecasermin is recombinant human insulin-like growth factor-1 (rhIGF-1) — a 70-amino-acid, 7,649 Da single-chain protein with three intramolecular disulfide bridges, produced in genetically modified E. coli, and sequence-identical to endogenous human IGF-1 (FDA label, section 11). It is not an analogue of anything. That distinction is the whole point.
Mecasermin is the one IGF-1 product that was actually developed, tested and approved as a medicine. It was approved by the FDA on 30 August 2005 under a priority review with orphan designation (NDA 021839, since deemed a BLA), and by the EMA on 2 August 2007 under exceptional circumstances. Both approvals cover one narrow indication in one small population: growth failure in children aged 2 and over with severe primary IGF-1 deficiency (SPIGFD), or with growth hormone gene deletion who have developed neutralizing antibodies to GH. The FDA definition of severe primary IGFD is quantitative and restrictive — height standard-deviation score ≤ −3.0 and basal IGF-1 SDS ≤ −3.0 and normal or elevated growth hormone. The label states its own limits plainly: INCRELEX “is not a substitute to GH for approved GH indications” and “is not indicated for use in patients with secondary forms of IGF-1 deficiency, such as GH deficiency, malnutrition, hypothyroidism, or chronic treatment with pharmacologic doses of anti-inflammatory corticosteroids.”
That approval does not extend one inch beyond those children. It does not cover short stature generally — a separate phase 3 program in broader growth failure was terminated for hypoglycemia (see below). It does not cover athletic, anabolic or anti-aging use. And it does not transfer to the IGF-1 analogues sold on the gray market: IGF-1 DES and IGF-1 LR3 are structurally different molecules, engineered specifically to escape the IGF-binding proteins that regulate this one, and neither has ever been given to a human being in a published study. Both of those pages argue hypoglycemia and mitogenic risk from first principles because no human data exists for them. Here, those same risks are documented in an approved label with a real safety database — and the buffering they were engineered to remove is precisely what makes mecasermin’s risks manageable.
One further identity trap, live in the literature: mecasermin rinfabate (iPlex) is a different product — rhIGF-1 complexed 1:1 with recombinant IGFBP-3. It was separately FDA-approved (BLA 021884, Insmed, 12 December 2005, priority/orphan), its EU application was withdrawn in March 2007 after the CHMP concluded the benefit had not been sufficiently demonstrated, and it is now Discontinued in the US, having been entangled in patent litigation with the Increlex sponsor 18Reference 18ReviewEfficacy and safety of mecasermin rinfabate — reviewView study →.
Findings for one are not findings for the other. The same caution applies to the rhIGF-1/rhIGFBP-3 complex studied in retinopathy of prematurity — a different formulation with its own, so far unpersuasive, evidence 19Reference 19Meta-analysisInsulin-like growth factor-1 for the prevention or treatment of retinopathy of prematurity — systematic review and meta-analysisView study →.
Support is an experimental score I’m building — a composite weighted by study type (human > animal > in vitro > review) and study volume. It’s a beta: a fast way to rank strength of evidence at a glance, not a validated metric. The low scores here mostly mean something different from the low scores on the analogue pages. For IGF-1 DES and IGF-1 LR3, low means never tested in a person. Here, three of the five applications were tested in randomized human trials and did not work — ALS most definitively. A null is a result, and it is scored as one. Each application links down to its write-up.
Human, and this is the approved indication. Severe primary IGF-1 deficiency is a rare disorder in which the GH receptor or its post-receptor signaling fails, so growth hormone is normal or high but IGF-1 is not made — Laron syndrome is the archetype. Giving GH is useless; giving the missing IGF-1 is the point.
The pivotal evidence is a multicenter, long-term, open-label program: 76 children with severe IGF-1 deficiency due to GH insensitivity, treated with rhIGF-1 at 60–120 µg/kg twice daily for up to 8 years. Height velocity roughly doubled in the first year and remained above baseline through year 8, with the effect dose-dependent 1Reference 1Long-term treatment with recombinant insulin-like growth factor (IGF)-I in children with severe IGF-I deficiency due to growth hormone insensitivity — human (multicentre, long-term, open-label; n=76, up to 8 years)View study →.
Registered as NCT00571727 (phase 2/3, n=92, 1991–2011) and complemented by NCT00125164 (phase 3, n=137, prepubertal children with growth failure from primary IGFD). Post-approval, the European Increlex Growth Forum Database (Eu-IGFD) registry has followed real-world use: an analysis of patients with and without Laron syndrome confirmed effectiveness and characterized safety in routine practice 2Reference 2Clinical trialEffectiveness and safety of rhIGF1 therapy in patients with or without Laron syndrome — human (observational registry)View study →; a further analysis examined pubertal timing and growth dynamics 4Reference 4Pubertal timing and growth dynamics in children with severe primary IGF-1 deficiency: results from the European Increlex Growth Forum Database Registry — human (registry)View study →; and a 2026 report gives near-adult height outcomes from real-world registry data — the outcome that actually matters for a growth drug 3Reference 3Clinical trialNear-adult height outcomes in patients treated with rhIGF-1 for severe growth failure: real-world IGFD registry data — human (multicentre observational registry)View study →.
Read the design honestly. This is not a placebo-controlled RCT program, and could not easily have been one in so rare a disease: the trials are open-label with historical or within-patient comparators. That is a recognized limitation, not a technicality. The independent French bulletin Prescrire reviewed mecasermin at launch and titled its assessment “Insufficient improvement in statural growth” 6Reference 6Mecasermin: new drugView study → — a dissenting appraisal from a source with no commercial stake, and it belongs here. The EMA’s own authorization was granted under exceptional circumstances because of the rarity of the condition. What is not in doubt is that treated children grow faster than they did untreated; what is contested is how much final adult height that buys, at what cost in hypoglycemia and monitoring.
A hard boundary that the trial record itself draws. Attempts to widen this indication have failed on safety. NCT00330668, a phase 3 in children and adolescents with growth failure associated with primary IGF-1 deficiency (n=114, 2005–2010), was terminated, with the sponsor’s stated reason recorded on ClinicalTrials.gov as “Unacceptable frequency of hypoglycemia observed at and above 200 ug/kg/day.” A combination program of rhGH plus rhIGF-1 in short stature associated with IGF-1 deficiency (NCT00572156, phase 2, n=106) was terminated for stated strategic reasons. The narrowness of the label is not regulatory timidity — it is where the drug stopped working safely.
Gap: No placebo-controlled RCT, and near-adult-height evidence is registry-derived rather than randomized. Nothing here supports use in idiopathic short stature, in secondary IGF-1 deficiency, or in anyone with closed epiphyses — all explicitly excluded by the label.
Human, off-label, and case-level. In the extreme insulin-resistance syndromes caused by biallelic INSR mutations — Rabson-Mendenhall syndrome and Donohue syndrome (leprechaunism) — insulin cannot signal, but IGF-1 can still act through the IGF-1 receptor and cross-talk to insulin-receptor pathways. rhIGF-1 is therefore mechanistically rational, and the reported outcomes are among the more striking in this literature: a 2015 report describes ten years of improved insulin resistance and growth in a patient with insulin-receptor mutations causing leprechaunism 17Reference 17Case reportTen-year improvement of insulin resistance and growth with recombinant human insulin-like growth factor 1 in a patient with insulin receptor mutations resulting in leprechaunism — human (case report)View study →; a 2016 report describes over five years of successful rhIGF1 treatment in a patient with a homozygous insulin-receptor mutation 16Reference 16Case reportSuccessful rhIGF1 treatment for over 5 years in a patient with severe insulin resistance due to homozygous insulin receptor mutation — human (case report)View study →; and a 2018 case report with an accompanying review synthesizes the published experience of mecasermin in insulin-receptor-related severe insulin resistance syndromes 15Reference 15Case reportMecasermin in insulin receptor-related severe insulin resistance syndromes: case report and review of the literature — human (case report + review)View study →.
This is real, and it is also the thinnest kind of real. These are individual patients in ultra-rare disease, published because they went well. There is no randomized trial, no controlled comparison, and — as always with case reports — no denominator: unsuccessful attempts are systematically less likely to be written up. A ClinicalTrials.gov query (v2 API, July 2026) for mecasermin or rhIGF-1 in severe insulin resistance, Rabson-Mendenhall or Donohue syndrome returned zero registered studies. Note also the direction of the pharmacology: this is the one setting where IGF-1’s glucose-lowering action is the desired effect rather than the dose-limiting one.
Gap: No controlled trial, no registry, no dose-finding. Publication bias is unquantifiable at this sample size. Nothing here generalizes to ordinary type 2 diabetes or garden-variety insulin resistance, which are not caused by insulin-receptor mutations.
Human, genuinely trialled, and largely negative. Rett syndrome is caused by MECP2 mutations, and IGF-1 signaling deficits in Mecp2-null mice made rhIGF-1 a rational candidate. The clinical program was real. A phase 1 open-label study (NCT01253317, n=12) established safety, pharmacokinetics and a preliminary efficacy signal in girls with Rett syndrome, reporting improvements in some breathing and mood measures 11Reference 11Safety, pharmacokinetics, and preliminary assessment of efficacy of mecasermin (recombinant human IGF-1) for the treatment of Rett syndrome — human (phase 1, open-label; n=12)View study →. A subsequent placebo-controlled crossover assessment of mecasermin (NCT01777542, phase 2, n=30, 2013–2016) provides the controlled read, and it did not deliver the phase 1 promise 12Reference 12RCTPlacebo-controlled crossover assessment of mecasermin for the treatment of Rett syndrome — human (placebo-controlled crossover trial)View study →. A 2025 systematic review of mecasermin for Rett syndrome pulls the program together and does not support it as an effective treatment 13Reference 13Systematic reviewMecasermin for the treatment of Rett syndrome: a systematic review — systematic review (human trials)View study →.
Where the story actually went matters here. The molecule that reached approval for Rett syndrome is trofinetide, a synthetic analogue of the IGF-1-derived tripeptide GPE — a different compound with a different mechanism and its own trial program. Mecasermin’s Rett data must not be read as trofinetide’s, or vice versa. (This is the same GPE / “(1-3)IGF-1” identity trap flagged on the IGF-1 DES page, arriving from the opposite direction.)
Gap: Small samples throughout — the controlled trial enrolled 30. No phase 3 of mecasermin in Rett syndrome exists, and the field has moved to a different molecule.
Human, definitively tested, and negative — this is the clearest null on the page. IGF-1 is a motor-neuron trophic factor, which made ALS an obvious target, and the compound got a fuller hearing there than in any indication except its own. A 1997 multicenter placebo-controlled study by the North America ALS/IGF-I Study Group reported an effect on progression that was modest and disputed 9Reference 9RCTEffect of recombinant human insulin-like growth factor-I on progression of ALSView study →. The definitive test came a decade later: NCT00035815, a phase 3, placebo-controlled, 2-year trial in 330 patients, completed 2007. Its published title states the result without hedging — “Subcutaneous IGF-1 is not beneficial in 2-year ALS trial” 8Reference 8RCTSubcutaneous IGF-1 is not beneficial in 2-year ALS trial — human (phase 3 RCT, n=330; null result)View study →. A Cochrane systematic review and meta-analysis of rhIGF-I for ALS/motor neuron disease reached a correspondingly unsupportive conclusion 10Reference 10Meta-analysisRecombinant human insulin-like growth factor I (rhIGF-I) for amyotrophic lateral sclerosis/motor neuron disease — systematic review and meta-analysisView study →.
This is why the score is 18% rather than 40%. The evidence volume is high — two RCTs, a large phase 3, a Cochrane review — and the answer is no. Read against the analogue pages, this is the single most useful data point on this hub: the trophic-factor rationale for IGF-1 was strong, mechanistically coherent, and supported by animal models, and it still failed when tested properly in people. Mechanistic plausibility is not efficacy.
Gap: None worth chasing for efficacy — the question was asked and answered. A residual gap remains in whether delivery route or a targeted subpopulation could change the answer, but nobody is pursuing subcutaneous rhIGF-1 in ALS on the strength of this record.
Human, randomized, and a split result. A 6-month randomized trial of rhIGF-1 in boys with Duchenne muscular dystrophy (registered as NCT01207908, phase 1/2, n=44) tested the anabolic hypothesis in the population where it is most clinically motivated. The result is in the title: rhIGF-1 therapy for 6 months improved growth but not motor function 14Reference 14RCTRecombinant human insulin-like growth factor-1 therapy for 6 months improves growth but not motor function in boys with Duchenne muscular dystrophy — human (RCT; motor-function null)View study →. Linear growth responded; the endpoint that determines whether a boy keeps walking did not.
That dissociation is the point, and it generalizes. IGF-1 reliably does what IGF-1 does — it drives statural and tissue growth. Whether that translates into functional muscle performance is a separate question, and in the one dystrophic population where it was tested with a control group, it did not. Anyone reasoning from “IGF-1 is anabolic” to “IGF-1 will improve my strength” is making exactly the inference this trial tested and refuted.
Gap: One trial, 6 months, small sample, one disease. It does not close the question for other muscle conditions — but it is the only randomized human muscle-function data that exists for rhIGF-1, and it is negative.
Mechanisms
| Target / pathway | Effect | Relevant to |
|---|---|---|
| Type-1 IGF receptor (IGF-1R) | Full agonist — mecasermin is sequence-identical to endogenous human IGF-1, not an analogue | All applications (FDA label §12.1) |
| Epiphyseal growth-plate chondrocytes | ↑ proliferation and calcification → statural growth until the plates fuse | The approved indication; also why closed epiphyses is a contraindication |
| Hepatic glucose output / peripheral glucose uptake | ↓ hepatic production, ↑ peripheral utilization, plus inhibition of insulin secretion → hypoglycemic potential | The documented dose-limiting toxicity |
| IGFBP-3 + acid-labile subunit ternary complex | Binds normally — >80% of circulating IGF-1 is held in this complex. Clearance is inversely proportional to IGFBP-3 | The physiological brake the gray-market analogues are engineered to remove |
| General mitogenic signaling | IGF-1 receptors are present on most cell types; IGF-1 has mitogenic activity increasing cell number | The labeled malignant-neoplasia contraindication |
| Lymphoid tissue | Growth of tonsillar and adenoidal tissue | Tonsillar hypertrophyobstructive sleep apnea |
Pharmacokinetics
Route is subcutaneous, twice daily, with food — and the food is not optional. The label states INCRELEX is administered by subcutaneous injection only; it must not be given intravenously, and injection sites are rotated between upper arm, thigh, buttock and abdomen to prevent lipohypertrophy. As a 7.6 kDa protein it has no meaningful oral bioavailability; there is no oral form and none is possible.
Absolute subcutaneous bioavailability is estimated close to 100% in healthy subjects, though it has not been determined in patients with primary IGFD. Mean terminal half-life is approximately 5.8 hours after a single 0.12 mg/kg subcutaneous dose in children with severe primary IGFD. Volume of distribution is roughly 0.257 ± 0.073 L/kg at a 0.045 mg/kg dose and rises with dose. IGF-1 is eliminated by both liver and kidney. (All figures: FDA label §12.3.)
The pharmacokinetically decisive fact is the binding proteins, and it is the hinge of this entire page. In blood, IGF-1 is bound to six IGFBPs, with more than 80% held as a complex with IGFBP-3 and an acid-labile subunit. Clearance is inversely proportional to IGFBP-3: the label quantifies CL/F at 0.04 L/hr/kg when IGFBP-3 is 0.5 µg/mL versus 0.01 L/hr/kg at 3 µg/mL. Patients with severe primary IGFD have greatly reduced IGFBP-3, which is why they clear IGF-1 faster than healthy people do. Read that against the analogues. IGF-1 DES and IGF-1 LR3 exist specifically to escape this complex, and are marketed on that escape as a potency advantage. What the ternary complex actually is, as the approved product’s own pharmacokinetics demonstrate, is a reservoir and a brake — the mechanism that keeps free IGF-1 low and its glucose-lowering action survivable. Removing it does not make an IGF safer or better-behaved; it delivers more unbuffered free ligand to the same receptors that produce the hypoglycemia documented below.
Clinical & regulatory status
Mecasermin is an approved prescription biologic and is currently marketed. Verified against Drugs@FDA / openFDA and the EMA in July 2026:
- United States: NDA 021839, approved 30 August 2005 as a Type 1 New Molecular Entity under priority review with orphan designation; deemed a BLA on 23 March 2020 under the biologics transition. Current marketing status: Prescription (active). The most recent Structured Product Label is effective 18 May 2026. Note a change many sources have not caught up with: Increlex was acquired from Ipsen by Eton Pharmaceuticals in December 2024 and relaunched in the US in January 2025 — Eton Pharmaceuticals, Inc. is the labeler on the current SPL, though the Drugs@FDA sponsor field still reads Ipsen.
- European Union: authorized 2 August 2007, under exceptional circumstances given the rarity of the condition, for long-term treatment of growth failure in children and adolescents with severe primary IGFD. Marketing authorization holder: Esteve Pharmaceuticals, S.A. The medicine remains under additional monitoring. Orphan designation was granted 22 May 2006 and removed from the Community register in August 2017 at the end of the 10-year market-exclusivity period — the designation lapsed on schedule; it was not revoked.
- Supply history — real, and worth knowing. The EMA maintained a supply-shortage page for Increlex (first published December 2013) which now records the shortage as resolved. The impact was concrete: the Increlex patient registry NCT00747604 (n=1,378) was terminated with the stated reason “Shortage of Increlex supply.” For a drug with no therapeutic alternative in its indication, supply is a clinical issue, not a commercial footnote.
- Not the same product: mecasermin rinfabate (iPlex), rhIGF-1 complexed with IGFBP-3, held its own US approval (BLA 021884, Insmed, 12 December 2005, priority/orphan) and is now Discontinued. Its EU application was withdrawn on 26 March 2007 after the CHMP found the benefit insufficiently demonstrated, citing manufacturing concerns, inadequate assessment of effectiveness and less than one year of treatment data 18Reference 18ReviewEfficacy and safety of mecasermin rinfabate — reviewView study →.
Prohibited in sport. IGF-1 and its analogues are banned at all times by the World Anti-Doping Agency under class S2 (peptide hormones, growth factors, related substances and mimetics). A prescription for an approved indication does not exempt an athlete; a Therapeutic Use Exemption would be required.
Registered trials (ClinicalTrials.gov v2 API, mecasermin as intervention, July 2026 — 37 records returned, of which the following are mecasermin/rhIGF-1 interventional studies):
| Completed | Ongoing | Terminated / withdrawn | Preclinical |
|---|---|---|---|
| ~18 | 3(incl. the IGFD global registry) | 8(incl. one for hypoglycemia, one for supply shortage) | Extensive |
Last checked: July 2026.
Sourcing, Route & Legal Status
This section is the inverse of every other page on this hub, and that is the point. Mecasermin has a legitimate, regulated, prescription supply chain. It is manufactured to pharmaceutical standard under a biologics license, released against pharmacopoeial identity, purity, potency, sterility and endotoxin specifications, distributed through licensed pharmacy channels, dispensed against a prescription, and subject to post-marketing pharmacovigilance and — in Europe — additional monitoring plus a patient registry. Adverse events go to a named marketing authorization holder and to the FDA. If a vial is out of specification, there is a recall mechanism and someone accountable for it.
Compare that with what the same molecule’s analogues are sold under. IGF-1 DES and IGF-1 LR3 come from unregulated peptide vendors, labeled “for research use only,” with no manufacturing oversight, no pharmacopoeial standard, no assurance the vial contains what the label says, and no accountable party. One analyzed black-market LR3 vial turned out to contain a His-tagged construct built for protein purification. There is no pharmaceutical-grade IGF-1 LR3 to divert, because none was ever made — whereas pharmaceutical-grade rhIGF-1 exists, and requires a pediatric endocrinologist to prescribe it for a condition you almost certainly do not have.
Legal status. Mecasermin is a prescription-only biologic in the US and EU. It is not a controlled substance, but supplying or obtaining it without a prescription is unlawful, and importing it for non-prescribed use is a customs and drug-law issue in most Western jurisdictions. Because it is an orphan biologic for a rare disease, it is expensive and access is routed through specialist pediatric endocrinology and payer prior-authorization rather than through any retail channel. No vendor is named or linked here, and there is no gray-market route to this product that would not be both illegal and, given the hypoglycemia profile below, dangerous without the glucose monitoring the label requires.
Administration. Subcutaneous injection only, twice daily, each dose within ±20 minutes of a meal or snack, using sterile disposable syringes, with injection-site rotation. Supplied as a multiple-dose vial containing 40 mg in 4 mL (10 mg/mL), preserved with benzyl alcohol. Solutions that are cloudy or contain particulate matter are not used.
Safety
Mecasermin is a specialist prescription drug whose risks are measured rather than inferred, and severe hypoglycemia is the dose-limiter — seizures and loss of consciousness occurred in the pivotal cohort, which is why every dose is tied to a meal. Malignancy is a hard contraindication, not a caveat.
- Severe hypoglycemia, including seizures. Reported by 42% of the trial cohort; the dose must be given within 20 minutes of a meal.
- Contraindicated in malignant neoplasia or a history of malignancy. Several cases were observed in treated children.
- Anaphylaxis and intracranial hypertension are labeled risks. Both require treatment interruption and urgent medical review.
- Contraindicated once growth plates have fused. There is no approved adult use, and it is not recommended in infants.
- Tonsillar and adenoidal hypertrophy. Occurred in 15% of trial subjects; periodic examination is required.
- Additive hypoglycemia with insulin and other glucose-lowering agents.
Full Safety & Interactions Detail
This is the most valuable section on the page, because — uniquely on this hub — these risks are measured rather than reasoned. Everything below comes from the FDA label for INCRELEX and from published trial and registry data. The clinical-trials safety population is 71 subjects with primary IGFD treated for a mean of 3.9 years, representing 274 subject-years.
- Hypoglycemia — the dose-limiter, and it is severe. The label’s first warning: “Severe hypoglycemia leading to hypoglycemic seizures has been observed with INCRELEX treatment.” In the trial cohort, hypoglycemia was reported by 30 of 71 subjects (42%) at least once; five had severe hypoglycemia requiring assistance and treatment, and four experienced hypoglycemic seizures or loss of consciousness on one or more occasions. Frequency was highest in the first month and in younger children. This is why the drug must be given within 20 minutes of a meal, why a missed meal means a withheld dose, why preprandial glucose monitoring is required during titration, and why the label tells patients to avoid driving and exercise for 2–3 hours after dosing. Registry data from Europe have since quantified the frequency and predictive factors of hypoglycemia in routine practice 5Reference 5Clinical trialFrequency and predictive factors of hypoglycemia in patients treated with rhIGF-1: data from the Eu-IGFD Registry — human (registry, safety)View study →. And the ceiling is documented independently: phase 3 trial NCT00330668 was terminated for “unacceptable frequency of hypoglycemia observed at and above 200 ug/kg/day.”
- Malignant neoplasia — a contraindication, not a caveat. INCRELEX is contraindicated in patients with malignant neoplasia or a history of malignancy. The label further warns that “several cases of malignant neoplasia have been observed in pediatric patients treated with INCRELEX” and directs that therapy be discontinued if evidence of malignancy develops. IGF-1 receptors are present on most cell types and IGF-1 is mitogenic (label §12.2). Note what this means for the analogues: the mitogenic concern that IGF-1 DES and IGF-1 LR3 can only frame as theoretical is, for the approved product, a hard contraindication backed by observed cases.
- Hypersensitivity and anaphylaxis. Contraindicated in known hypersensitivity. Post-marketing reactions range from local injection-site reactions to systemic anaphylaxis requiring hospitalization; a published case report documents anaphylaxis to rhIGF-1 7Reference 7Case reportAnaphylactic reaction to recombinant insulin-like growth factor-I — human (case report)View study →. Treatment is interrupted and urgent medical attention sought.
- Intracranial hypertension. Occurred in three trial subjects, with papilledema, visual changes, headache, nausea and vomiting; signs resolved after interruption. Funduscopic examination is recommended at initiation and periodically.
- Tonsillar and adenoidal hypertrophy. Noted in 11 of 71 subjects (15%) in the first 1–2 years. Seven required tonsillectomy or adenotonsillectomy; three of those had obstructive sleep apnea, which resolved after surgery in all three. Periodic examination is required. Thymus hypertrophy was also reported.
- Slipped capital femoral epiphysis and scoliosis progression. Any child developing a limp or hip/knee pain must be evaluated for SCFE and osteonecrosis; any child with scoliosis must be monitored for curve progression. Both are recognized hazards of rapid growth.
- Closed epiphyses. Contraindicated for growth promotion once the growth plates have fused — which is to say, in every adult. There is no approved adult use of this drug.
- Benzyl alcohol / infants. The formulation is preserved with benzyl alcohol, associated with serious adverse reactions including death in neonates and infants. Use in infants is not recommended, and safety and effectiveness are not established below 2 years of age.
- Other trial adverse reactions (≥5%): lipohypertrophy, bruising, otitis media and serous otitis media, snoring, headache, dizziness, convulsions, vomiting, hypoacusis and middle-ear fluid, cardiac murmur, arthralgia and limb pain.
- Interactions. Additive hypoglycemia with insulin and other glucose-lowering agents is the mechanistically expected interaction and follows directly from the labeled hypoglycemic effect. Dosing is coordinated with meals rather than with other drugs.
- Who should not take it. Anyone with active or previous malignancy; anyone with closed epiphyses; anyone with known hypersensitivity to mecasermin or excipients; infants; and — in practice — anyone who does not have severe primary IGF-1 deficiency, since there is no indication, no dose and no favorable risk-benefit outside it.
Scope disclosure (honesty, not a claim):
- Human data? Yes — and that is what distinguishes it from the rest of its cluster. An approved indication with a pivotal multi-year program, post-marketing registries, and randomized trials in four further conditions. Note that the pivotal growth program is open-label, not placebo-controlled.
- Interactions assessed? Partially. The hypoglycemia mechanism and its interaction with meals are labeled and quantified; formal drug-drug interaction studies are limited, and additive risk with glucose-lowering agents is mechanistic rather than trial-derived.
- Pregnancy/lactation assessed? No. No human data; animal reproductive toxicology is reassuring as far as it goes, which is not far.
- Long-term safety established? Partially. 274 subject-years in the pivotal cohort plus multi-year European registry follow-up is a genuine safety database — far better than anything on the analogue pages — but it is a pediatric database in a rare disease at labeled doses. It says nothing about adults, other doses, or other purposes.
The absence-of-evidence rule still applies at the edges: where mecasermin has not been studied — adults, healthy people, athletic use, any dose above the labeled maximum — “not assessed” is the correct statement, not “safe.”
Not established. The label states there are no available data on INCRELEX use in pregnant women, and notes that exposure during pregnancy is unlikely because the drug is not indicated after epiphyseal closure. In animal reproduction studies, no embryo-fetal developmental abnormalities were observed with intravenous administration to pregnant rats and rabbits during organogenesis at exposures up to 11-fold and 3-fold the maximum recommended human dose respectively, on a body-surface-area basis. Lactation data are absent. Given that the approved population is prepubertal and peripubertal children with open growth plates, this is not a realistic exposure scenario for the labeled indication — and there is no basis for use in pregnancy outside it.
Dosage
The dosing below is the approved pediatric regimen, reproduced as regulatory fact rather than as guidance, and it is not transferable to any other person or purpose. From the FDA label: treatment must be supervised by a physician experienced in diagnosing and managing pediatric patients with short stature due to severe primary IGF-1 deficiency or GH gene deletion with neutralizing antibodies to GH, and the dose is individualized.
- Starting dose: 0.04–0.08 mg/kg body weight twice daily by subcutaneous injection.
- Titration: if well tolerated for at least one week, increase by 0.04 mg/kg per dose.
- Maximum: 0.12 mg/kg twice daily.
- Timing: each dose within ±20 minutes of a meal or snack. If the patient cannot eat, the dose is withheld.
- Missed doses: never doubled up. “The dose of INCRELEX should never be increased to make up for one or more omitted doses.”
- Monitoring: preprandial glucose monitoring at initiation and until a well-tolerated dose is established; funduscopic examination at initiation and periodically; periodic examination for tonsillar/adenoidal hypertrophy; evaluation of any limp or hip/knee pain.
Why none of this converts into a dose for anyone else. The regimen is calibrated to children with severe primary IGF-1 deficiency, whose IGFBP-3 is greatly reduced and who therefore clear IGF-1 faster than a person with normal binding proteins — the label makes clearance an explicit function of IGFBP-3. Someone with normal IGFBP-3 has entirely different pharmacokinetics. Beyond that, the hypoglycemia ceiling is empirical and low: a phase 3 program was terminated at and above 200 µg/kg/day, which is only modestly above the labeled maximum. There is no established dose for adults, for muscle-building, for anti-aging, or for any off-label purpose, and none is supplied. The safety architecture that makes the labeled dose acceptable — glucose monitoring, meal timing, funduscopy, specialist supervision — is inseparable from the number.
References
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